This invention relates to a plural frequency antenna used in an emergency position indicating radio beacon.
Emergency position indicating radio beacons (EPIRBs) are intended for use by mariners in an emergency situation. According to international agreements, the EPIRB transmits a homing signal on 121.5 mhz only or on both 121.5 and 243 mhz, as well as a satellite beacon signal on 406 mhz. In the event of an accident at sea or other distress situation, the EPIRB is manually deployed or, in the event there is no opportunity for manual deployment, automatically deployed in order to transmit the homing and satellite signal frequencies. The 121.5 mhz and 243 mhz signals are transmitted to ground based and other rescue facilities. Air and sea search and rescue (SAR) vehicles are able to home-in on the signals and thus locate the EPIRB and those in distress.
The EPIRB also transmits a 406 mhz identification signal which is received by a search and rescue satellite-aided tracking (SARSAT) satellites which are in orbit around the earth. The SARSAT is able to determine the position coordinates of the EPIRB by doppler shift techniques and to transmit the position of the EPIRB to one of several ground receiving stations located around the globe. The ground receiving station relays the position coordinates of the EPIRB as well as identification information relating to the vessel to which the EPIRB is assigned to a Mission Control Center (MCC). The MCC sends the location of the EPIRB to a rescue coordination center which deploys ships, planes, or helicopters as appropriate to the EPIRB site in order to provide rescue operations.
The EPIRB itself is housed in a buoy which is designed to float on the surface of the water. The upper portion of the buoy includes an antenna cone which contains the transmitting antenna for the buoy; and in order to aid in visual location of the EPIRB in the water by the SAR vehicles, the tip of the antenna cone is provided with a light. In order to function properly, the EPIRB antenna must efficiently transmit the three signals at 121.5, 243, and 406 mhz as well as provide DC power to the lamp on the top of the antenna.